Join or match value from two tables - sql

Question

I have two tables . Based on the first table I need to check if it is locked or not.
In the below example , if the combination is present then I would pick else it should match with 'All' and bring that record.
Lock Table
Transaction Table
Output
Query tried - But it is doing a cross join . I understand the reason but could not solve it
SELECT a.GROUP,a.OFFICE,b.LOCK
FROM T_ITEMS a INNER JOIN LOCKED_T b
ON a.ORG=c.ORG
AND (a.OFFICE =b.OFFICE OR b.OFFICE='All')
AND a.GROUP=b.GROUP

Answer 1

What you want to do is match on group or use all as a "wildcard". The problem is that you are matching on both for one of the items -- so you get two results.
So what you do is the first join
SELECT a.GROUP, a.OFFICE, b.LOCK
FROM T_ITEMS a
LEFT JOIN LOCKED_T b ON a.ORG = c.ORG A
AND a.OFFICE = b.OFFICE
AND a.GROUP = b.GROUP
Now take those results and try to fill in the missing ones (missing ones will have a null in the lock column
SELECT
BASE.GROUP, BASE.OFFICE, COLLESCE(BASE.LOCK, L.LOCK) AS LOCK
FROM
(SELECT
a.GROUP, a.OFFICE, b.LOCK
FROM
T_ITEMS a
LEFT JOIN
LOCKED_T b ON a.ORG = c.ORG
AND a.OFFICE = b.OFFICE
AND a.GROUP = b.GROUP) BASE
LEFT JOIN
LOCKED_T L ON BASE.ORG = L.ORG
AND L.OFFICE = 'All'
AND base.GROUP = L.GROUP
AND BASE.LOCK IS NULL

Answer 2

I look at this as a "defaulting" problem. That can be solved with two left joins:
SELECT i.GROUP, i.OFFICE,
COALESCE(l.LOCK, l_default.LOCK)
FROM T_ITEMS i LEFT JOIN
LOCKED_T l
ON l.ORG = i.ORG AND l.OFFICE = i.OFFICE LEFT JOIN
LOCKED_T l_default
ON l_default.OFFICE = 'All' AND l_default.GROUP = i.GROUP AND l.ORG IS NULL;
As the number of combinations grows, this gets trickier. So a more generalizable alternative uses a correlated subquery:
SELECT i.*,
(SELECT MAX(l.LOCK) KEEP (DENSE_RANK FIRST ORDER BY NULLIF(l.OFFICE, 'All) NULLS LAST,NULLIF(l.GROUP, 'All) NULLS LAST
FROM LOCKED_T l
WHERE (l.OFFICE = i.OFFICE OR l.OFFICE = 'All') AND
(l.GROUP = i.GROUP OR l.GROUP = 'All')
) as LOCKED
FROM T_ITEMS i;
Oracle 12C supports lateral joins so this can actually be in the FROM clause instead.